U.S. patent application number 12/999731 was filed with the patent office on 2012-09-27 for ion sources, systems and methods.
This patent application is currently assigned to CARL ZEISS NTS, LLC.. Invention is credited to Mark D. DiManna, Alexander Groholski, John Notte, VI, Colin A. Sanford, Billy W. Ward.
Application Number | 20120241640 12/999731 |
Document ID | / |
Family ID | 40416893 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120241640 |
Kind Code |
A1 |
Ward; Billy W. ; et
al. |
September 27, 2012 |
ION SOURCES, SYSTEMS AND METHODS
Abstract
Ion sources, systems and methods are disclosed. In some
embodiments, the ion sources, systems and methods can exhibit
relatively little undesired vibration and/or can sufficiently
dampen undesired vibration. This can enhance performance (e.g.,
increase reliability, stability and the like).
Inventors: |
Ward; Billy W.; (Boyce,
LA) ; Sanford; Colin A.; (Atkinson, NH) ;
Notte, VI; John; (Gloucester, MA) ; Groholski;
Alexander; (Salem, MA) ; DiManna; Mark D.;
(Fremont, NH) |
Assignee: |
CARL ZEISS NTS, LLC.
Peabody
MA
|
Family ID: |
40416893 |
Appl. No.: |
12/999731 |
Filed: |
June 20, 2008 |
PCT Filed: |
June 20, 2008 |
PCT NO: |
PCT/US2008/067718 |
371 Date: |
June 3, 2011 |
Current U.S.
Class: |
250/396R ;
250/423R; 250/493.1 |
Current CPC
Class: |
H01J 37/28 20130101;
H01J 2237/244 20130101; H01J 2237/2826 20130101; H01J 2237/2487
20130101; H01J 2237/002 20130101; H01J 2237/024 20130101; H01J
37/08 20130101; H01J 2237/0216 20130101; F25D 19/006 20130101; H01J
2237/0807 20130101; H01J 27/26 20130101; H01J 37/265 20130101; H01J
2237/0805 20130101; H01J 37/067 20130101; H01J 2237/061
20130101 |
Class at
Publication: |
250/396.R ;
250/423.R; 250/493.1 |
International
Class: |
H01J 27/02 20060101
H01J027/02; H01J 3/26 20060101 H01J003/26; G21K 5/04 20060101
G21K005/04 |
Claims
1.-63. (canceled)
64. A field emission charged particle source, comprising: an outer
structure mounted to a carrying structure being at environmental
temperature, the outer structure comprising a material having a
thermal conductivity; an intermediate structure mounted to the
outer structure, the intermediate structure comprising a material
having a thermal conductivity; an inner structure mounted to the
intermediate structure, the inner structure comprising a material
having a thermal conductivity; a charged particle field emitter
mounted to the inner structure; and a cooling device thermally
connected to the intermediate structure, wherein: the outer
structure comprises a material having a lower thermal conductivity
than the material of the inner structure, and/or the material of
the intermediate structure has a thermal conductivity that is
larger than 1.5 times the thermal conductivity of the material of
the outer structure; the cooling device is thermally connected to
the intermediate structure along a first bundle of thermally
conducting, flexible wires; and the cooling device is connected to
the intermediate structure along a second bundle of flexible wires
and along one or more rigid rods.
65. The field emission charged particle source of claim 64, wherein
the outer structure has a first wall thickness, the inner structure
has a second wall thickness, and the first wall thickness is less
than the second wall thickness.
66. The field emission charged particle source of claim 64, wherein
the inner structure comprises copper and the outer structure
comprises stainless steel.
67. The field emission charged particle source of claim 64, wherein
the outer structure has a cylindrical shape with a first diameter,
the inner structure has a cylindrical shape with a second diameter,
and the second diameter is less than the first diameter.
68. The field emission charged particle source of claim 64, wherein
the one or more rigid rods are arranged, in series, between the
first and the second bundle of thermally conductive flexible
wires.
69. The field emission charged particle source of claim 64, wherein
the first and/or the second bundle of flexible wires comprise
copper.
70. The field emission charged particle source of claim 64, wherein
the first and/or the second bundle of flexible wires comprise a
carbonated pitch material.
71. The field emission charged particle source of claim 64, wherein
the one or more rigid rods comprise copper.
72. The field emission charged particle source of claim 64, further
comprising an extraction electrode electrically isolated from the
field emitter, wherein, during operation of the field emission
charged particle source, a high voltage is applied between the
field emitter and the extraction electrode.
73. The field emission charged particle source of claim 64, wherein
the field emitter is mounted to the inner structure via a material
with a thermal conductivity which is greater than the thermal
conductivity of the material of the outer structure.
74. The field emission charged particle source of claim 64, further
comprising a gas conducting tube configured to feed a gas to a
region within the inner structure, wherein the gas conducting tube
terminates in an intermediate region between the outer and the
inner structures, and the inner structure comprises holes
configured to provide a gas flow from the intermediate region to a
region surrounded by the inner structure.
75. The field emission charged particle source of claim 74, further
comprising a control configured to switch off the cooling device
for a defined period of time.
76. The field emission charged particle source of claim 75, wherein
the cooling device is thermally connected to the intermediate
structure isothermically.
77. The field emission charged particle source of claim 76, wherein
the inner structure is a cylinder, the intermediate structure is a
ring, and the cooling device is thermally connected to the
intermediate structure along a series of connection regions which
are arranged along the intermediate structure.
78. The field emission charged particle source of claim 64, wherein
the outer structure comprises a material having a lower thermal
conductivity than the material of the inner structure.
79. The field emission charged particle source of claim 78, wherein
the material of the intermediate structure has a thermal
conductivity that is larger than 1.5 times the thermal conductivity
of the material of the outer structure.
80. The field emission charged particle source of claim 74, wherein
the material of the intermediate structure has a thermal
conductivity that is larger than 1.5 times the thermal conductivity
of the material of the outer structure.
81. A gas field beam system, comprising: a field emission charged
particle source according to claim 64, the field emission charged
particle being configured to generate a beam of charged particles
with a main direction of propagation; a scanning system configured
to deflect the beam of charged particles in a direction
perpendicular to the main direction of propagation; and a control
system configured to operate the field emission charged particle
source, the control system being configured to provide at least a
first mode of operation and a second mode of operation, wherein: in
the first mode of operation, the cooling device is operated to cool
the field emitter; in the second mode of operation, the cooling
device is off; and in the second mode of operation, the scanning
system is operated so that the beam is deflected to scan a
sample.
82. A system, comprising: a tip configured to cause ionization of
gas particles to form an ion beam, the tip being mounted on a
support structure; and a vibrational damper connected to the
support structure and to a cooling device, the vibrational damper
comprising: a first plurality of flexible members connected to the
support structure, a second plurality of flexible members connected
to the cooling device, and a solid member disposed between the
first and second pluralities of flexible members.
Description
TECHNICAL FIELD
[0001] This disclosure relates to ion sources, systems, and
methods.
BACKGROUND
[0002] Ion sources and systems can produce ion beams which are used
to investigate and/or modify a sample.
SUMMARY
[0003] In some embodiments, the ion sources, systems and methods
can exhibit relatively little undesired vibration and/or can
sufficiently dampen undesired vibration. This can enhance
performance (e.g., increase reliability, stability and the
like).
[0004] In one aspect, the disclosure features a field emission
charged particle source that includes: (a) an outer structure
mounted to a carrying structure being at environmental temperature;
(b) an intermediate structure mounted to the outer structure; (c)
an inner structure mounted to the intermediate structure; (d) a
charged particle emitter mounted to the inner structure; and (c) a
cooling device thermally connected to the intermediate structure.
The outer structure is made of a material having at cryostatic
temperature a lower thermal conductivity than the material of the
inner structure.
[0005] In another aspect, the disclosure features a field emission
charged particle source that includes: (a) an outer structure
mounted to a carrying structure being at environmental temperature,
the outer structure having a thermal conductivity; (b) an
intermediate structure mounted to the outer structure; (c) an inner
structure mounted to the intermediate structure; (d) a field
emitter mounted to the inner structure; and (e) a cooling device
thermally connected to the intermediate structure. The intermediate
structure has a thermal capacity which is larger than 1.5 times the
thermal conductivity of the outer structure.
[0006] In a further aspect, the disclosure features a gas field
beam system that includes: (a) a field emitting source generating a
beam of charged particles with a main direction of propagation; (b)
a cooler thermally connected to the field emitter or a structure to
which the field emitter is mounted; (c) a scanning system by the
aid of which a beam generated by the field emission source can be
deflected in direction perpendicular to the main direction of
propagation; and (d) a control system for operating the field
emission system, the control system providing at least a first and
a second mode of operation. In the first mode of operation the
cooler is operated to cool the field emitter, and in the second
mode of operation the cooler is switched off and the scanning
system is operated so that beam is deflected to scan a sample.
[0007] In another aspect, the disclosure features a gas field beam
system that includes: (a) a field emitting source generating a beam
of charged particles with a main direction of propagation; (b) a
cooler thermally connected to the field emitter or a structure to
which the field emitter is mounted; (c) a scanning-system by the
aid of which a beam generated by the field emission source can be
deflected in direction perpendicular to the main direction of
propagation; and (d) a control system for operating the field
emission system, the control system providing at least a first and
a second mode of operation. In the first mode of operation the
cooler is operated to cool the field emitter, and in the second
mode of operation the cooler is switched off and the scanning
system is operated so that beam is deflected to scan a sample.
[0008] In a further aspect, the disclosure features a method that
includes exposing a sample to a charged particle beam generated by
a tip of a charged particle system, where during exposure of the
sample, a constant phase is maintained between a vibrational
displacement function of the tip and corresponding portions of an
exposure pattern of the charged particle beam on the sample.
[0009] In another aspect, the disclosure features a system that
includes a tip configured to cause ionization of gas particles to
form an ion beam, the tip being mounted on a support structure, and
a vibrational damper connected to the support structure and to a
cooling device, where the vibrational damper includes a first
plurality of flexible members connected to the support structure, a
second plurality of flexible members connected to the cooling
device, and a solid member disposed between the first and second
pluralities of flexible members.
[0010] In a further aspect, the disclosure features an ion
microscope system that includes a first member that includes a
first curved surface, and a second member connected to a tip and
including a second curved surface complementary to the first curved
surface and configured to permit relative motion between the first
and second members, where the second curved surface includes a
plurality of annular protrusions, and where when the first and
second members are drawn together, at least some of the annular
protrusions contact the first curved surface to form annular
contact regions between the first and second surfaces.
[0011] Embodiments can include one or more of the following
features.
[0012] The outer structure can have a first wall thickness and the
inner structure can have a second wall thickness, where the first
wall thickness is smaller than the second wall thickness.
[0013] The inner structure can be made of copper and the outer
structure can be made of stainless steel.
[0014] The outer structure can have a cylindrical shape with a
first diameter and the inner structure can have a cylindrical shape
with a second diameter, the second diameter being smaller than the
first diameter.
[0015] The cooling device can be thermally connected to the
intermediate structure along a first bundle of thermally
conducting, flexible wires. The cooling device can be connected to
the intermediate structure along a second bundle of flexible wires
and along one or more rigid rods, where the one or more rigid rods
are arranged, in series, between the first and the second bundle of
thermally conductive flexible wires. The first and/or the second
bundle of flexible wires can be made of copper. The first and/or
the second bundle of flexible wires can be made of a carbonated
pitch material. The rigid rod can include copper.
[0016] The charged particle source can include an extraction
electrode electrically isolated from the field emitter and where,
in operation, a high voltage is applied between the field emitter
and the extraction electrode.
[0017] The field emitter can be mounted to the inner structure via
a material with a thermal conductivity which is higher than the
thermal conductivity of the material of the outer structure.
[0018] The field emission charged particle source can include a gas
conducting tube for feeding a gas to a region within the inner
structure, the gas conducting tube terminating in an intermediate
region between the outer and the inner structure, and the inner
structure comprising holes to provide a gas flow from the
intermediate region to a region surrounded by the inner
structure.
[0019] The field emission charged particle source can include a
control by which the cooling device can be switched off for a
defined period of time.
[0020] The cooling device can be thermally connected to the
intermediate structure isothermically.
[0021] The inner structure can be a cylinder, where the
intermediate structure has the form of a ring and where the cooling
device is thermally connected to the intermediate structure along a
series of connection regions which are arranged along the
intermediate structure.
[0022] The outer structure can be made of a material having at
cryostatic temperature a lower thermal conductivity than the
material of the inner structure.
[0023] The details of one or more embodiments are set forth in the
accompanying drawings and the description below. Other features and
advantages will be apparent from the description, drawings, and
claims.
DESCRIPTION OF DRAWINGS
[0024] FIG. 1 is a schematic diagram of an ion microscope
system.
[0025] FIG. 2 is a schematic diagram of a gas field ion source.
[0026] FIG. 3 is a schematic diagram of a portion of an ion
microscope system that includes a vibration damper.
[0027] FIG. 4 is a schematic diagram of another embodiment of a
vibration damper.
[0028] FIGS. 5A and 5B are schematic diagrams of images of a line
of material on a sample surface.
[0029] FIG. 6A is a schematic diagram of the vibrational amplitude
of a tip.
[0030] FIG. 6B is a schematic diagram of a sample image.
[0031] FIG. 7 is a schematic diagram showing phase-locking of an
image scan sequence to a vibrational displacement function of a
tip.
[0032] FIG. 8 is a schematic diagram of a tip manipulator.
[0033] FIG. 9 is a schematic diagram of a portion of a tip
manipulator.
[0034] FIG. 10 is a schematic diagram of a portion of a tip
manipulator.
[0035] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
Introduction
[0036] When used to investigate properties of various samples, ion
beams can provide qualitative and/or quantitative measurements that
are precise and accurate to atomic resolution. Sample images
measured with an ion beam (e.g., images that are derived from
measurements of secondary electrons and/or scattered ions and/or
scattered neutral atoms) can have very high resolution, revealing
sample features that are difficult to observe using other imaging
techniques. Optionally, ion beams can be used to provide
qualitative and/or quantitative material constituent information
about a sample.
[0037] An example of a sample is a semiconductor article.
Semiconductor fabrication typically involves the preparation of an
article (a semiconductor article) that includes multiple layers of
materials sequentially deposited and processed to form an
integrated electronic circuit, an integrated circuit element,
and/or a different microelectronic device. Such articles typically
contain various features (e.g., circuit lines formed of
electrically conductive material, wells filled with electrically
non-conductive material, regions formed of electrically
semiconductive material) that are precisely positioned with respect
to each other (e.g., generally on the scale of within a few
nanometers). The location, size (length, width, depth), composition
(chemical composition) and related properties (conductivity,
crystalline orientation, magnetic properties) of a given feature
can have an important impact on the performance of the article. For
example, in certain instances, if one or more of these parameters
is outside an appropriate range, the article may be rejected
because it cannot function as desired. As a result, it is generally
desirable to have very good control over each step during
semiconductor fabrication, and it would be advantageous to have a
tool that could monitor the fabrication of a semiconductor article
at various steps in the fabrication process to investigate the
location, size, composition and related properties of one or more
features at various stages of the semiconductor fabrication
process. As used herein, the term semiconductor article refers to
an integrated electronic circuit, an integrated circuit element, a
microelectronic device or an article formed during the process of
fabricating an integrated electronic circuit, an integrated circuit
element, a microelectronic device. In some embodiments, a
semiconductor article can be a portion of a flat panel display or a
photovoltaic cell. Regions of a semiconductor article can be formed
of different types of material (electrically conductive,
electrically non-conductive, electrically semiconductive).
Exemplary electrically conductive materials include metals, such as
aluminum, chromium, nickel, tantalum, titanium, tungsten, and
alloys including one or more of these metals (e.g., aluminum-copper
alloys). Metal silicides (e.g., nickel silicides, tantalum
silicides) can also be electrically conductive. Exemplary
electrically non-conductive materials include borides, carbides,
nitrides, oxides, phosphides, and sulfides of one or more of the
metals (e.g., tantalum borides, tantalum gennaniums, tantalum
nitrides, tantalum silicon nitrides, and titanium nitrides).
Exemplary electrically semiconductive materials include silicon,
germanium and gallium arsenide. Optionally, an electrically
semiconductive material can be doped (p-doped, n-doped) to enhance
the electrical conductivity of the material. Typical steps in the
deposition/processing of a given layer of material include imaging
the article (e.g., to determine where a desired feature to be
formed should be located), depositing an appropriate material
(e.g., an electrically conductive material, an electrically
semiconductive material, an electrically non-conductive material)
and etching to remove unwanted material from certain locations in
the article. Often, a photoresist, such as a polymer photoresist,
is deposited/exposed to appropriate radiation/selectively etched to
assist in controlling the location and size of a given feature.
Typically, the photoresist is removed in one or more subsequent
process steps, and, in general, the final semiconductor article
desirably does not contain an appreciable amount of
photoresist.
[0038] FIG. 1 shows a schematic diagram of a gas field ion
microscope system 100 that includes a gas source 110, a gas field
ion source 120, ion optics 130, a sample manipulator 140, a
front-side detector 150, a back-side detector 160, and an
electronic control system 170 (e.g., an electronic processor, such
as a computer) electrically connected to various components of
system 100 via communication lines 172a-172f. A sample 180 is
positioned in/on sample manipulator 140 between ion optics 130 and
detectors 150, 160. During use, an ion beam 192 is directed through
ion optics 130 to a surface 181 of sample 180, and particles 194
resulting from the interaction of ion beam 192 with sample 180 are
measured by detectors 150 and/or 160.
[0039] As shown in FIG. 2, gas source 110 is configured to supply
one or more gases 182 to gas field ion source 120. Gas source 110
can be configured to supply the gas(es) at a variety of purities,
flow rates, pressures, and temperatures. In general, at least one
of the gases supplied by gas source 110 is a noble gas (helium
(He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe)), and ions of
the noble gas are desirably the primary constituent in ion beam
192. In general, as measured at surface 181 of sample 180, the
current of ions in ion beam 192 increases monotonically as the
pressure of the noble gas in system 100 increases. In certain
embodiments, this relationship can be described by a power law
where, for a certain range of noble gas pressures, the current
increases generally in proportion to gas pressure.
[0040] Optionally, gas source 110 can supply one or more gases in
addition to the noble gas(es); an example of such a gas is
nitrogen. Typically, while the additional gas(es) can be present at
levels above the level of impurities in the noble gas(es), the
additional gas(es) still constitute minority components of the
overall gas mixture introduced by gas source 110.
[0041] Gas field ion source 120 is configured to receive the one or
more gases 182 from gas source 110 and to produce gas ions from
gas(es) 182. Gas field ion source 120 includes an electrically
conductive tip 186 with a tip apex 187, an extractor 190 and
optionally a suppressor 188.
[0042] Electrically conductive tip 186 can be formed of various
materials. In some embodiments, tip 186 is formed of a metal (e.g.,
tungsten (W), tantalum (Ta), iridium (Ir), rhenium (Rh), niobium
(Nb), platinum (Pt), molybdenum (Mo)). In certain embodiments,
electrically conductive tip 186 can be formed of an alloy. In some
embodiments, electrically conductive tip 186 can be formed of a
different material (e.g., carbon (C)).
[0043] During use, tip 186 is biased positively (e.g.,
approximately 20 kV) with respect to extractor 190, extractor 190
is negatively or positively biased (e.g., from -20 kV to +50 kV)
with respect to an external ground, and optional suppressor 188 is
biased positively or negatively (e.g., from -5 kV to +5 kV) with
respect to tip 186. Because tip 186 is formed of an electrically
conductive material, the electric field of tip 186 at tip apex 187
points outward from the surface of tip apex 187. Due to the shape
of tip 186, the electric field is strongest in the vicinity of tip
apex 187. The strength of the electric field of tip 186 can be
adjusted, for example, by changing the positive voltage applied to
tip 186. With this configuration, un-ionized gas atoms 182 supplied
by gas source 110 are ionized and become positively-charged ions in
the vicinity of tip apex 187. The positively-charged ions are
simultaneously repelled by positively charged tip 186 and attracted
by negatively charged extractor 190 such that the
positively-charged ions are directed from tip 186 into ion optics
130 as ion beam 192. Suppressor 188 assists in controlling the
overall electric field between tip 186 and extractor 190 and,
therefore, the trajectories of the positively-charged ions from tip
186 to ion optics 130. In general, the overall electric field
between tip 186 and extractor 190 can be adjusted to control the
rate at which positively-charged ions are produced at tip apex 187,
and the efficiency with which the positively-charged ions are
transported from tip 186 to ion optics 130.
[0044] In general, ion optics 130 are configured to direct ion beam
192 onto surface 181 of sample 180. Ion optics 130 can, for
example, focus, collimate, deflect, accelerate, and/or decelerate
ions in beam 192. Ion optics 130 can also allow only a portion of
the ions in ion beam 192 to pass through ion optics 130. Generally,
ion optics 130 include a variety of electrostatic and other ion
optical elements that are configured as desired. By manipulating
the electric field strengths of one or more components (e.g.,
electrostatic deflectors) in ion optics 130, He ion beam 192 can be
scanned across surface 181 of sample 180. For example, ion optics
130 can include two deflectors that deflect ion beam 192 in two
orthogonal directions. The deflectors can have varying electric
field strengths such that ion beam 192 is rastered across a region
of surface 181.
[0045] When ion beam 192 impinges on sample 180, a variety of
different types of particles 194 can be produced. These particles
include, for example, secondary electrons, Auger electrons,
secondary ions, secondary neutral particles, primary neutral
particles, scattered ions and photons (e.g., X-ray photons, IR
photons, visible photons, UV photons). Detectors 150 and 160 are
positioned and configured to each measure one or more different
types of particles resulting from the interaction between He ion
beam 192 and sample 180. As shown in FIG. 1, detector 150 is
positioned to detect particles 194 that originate primarily from
surface 181 of sample 180, and detector 160 is positioned to detect
particles 194 that emerge primarily from surface 183 of sample 180
(e.g., transmitted particles). As described in more detail below,
in general, any number and configuration of detectors can be used
in the microscope systems disclosed herein. In some embodiments,
multiple detectors are used, and some of the multiple detectors are
configured to measure different types of particles. In certain
embodiments, the detectors are configured to provide different
information about the same type of particle (e.g., energy of a
particle, angular distribution of a given particle, total abundance
of at given particle). Optionally, combinations of such detector
arrangements can be used.
[0046] In general, the information measured by the detectors is
used to determine information about sample 180. Typically, this
information is determined by obtaining one or more images of sample
180. By rastering ion beam 192 across surface 181, pixel-by-pixel
information about sample 180 can be obtained in discrete steps.
Detectors 150 and/or 160 can be configured to detect one or more
different types of particles 194 at each pixel.
[0047] The operation of microscope system 100 is typically
controlled via electronic control system 170. For example,
electronic control system 170 can be configured to control the
gas(es) supplied by gas source 110, the temperature of tip 186, the
electrical potential of tip 186, the electrical potential of
extractor 190, the electrical potential of suppressor 188, the
settings of the components of ion optics 130, the position of
sample manipulator 140, and/or the location and settings of
detectors 150 and 160. Optionally, one or more of these parameters
may be manually controlled (e.g., via a user interface integral
with electronic control system 170). Additionally or alternatively,
electronic control system 170 can be used (e.g., via an electronic
processor, such as a computer) to analyze the information collected
by detectors 150 and 160 and to provide information about sample
180 (e.g., topography information, material constituent
information, crystalline information, voltage contrast information,
optical property information, magnetic information), which can
optionally be in the form of an image, a graph, a table, a
spreadsheet, or the like. Typically, electronic control system 170
includes a user interface that features a display or other kind of
output device, an input device, and a storage medium.
[0048] In certain embodiments, electronic control system 170 can be
configured to control various properties of ion beam 192. For
example, control system 170 can control a composition of ion beam
192 by regulating the flow of gases into gas field ion source 120.
By adjusting various potentials in ion source 120 and ion optics
130, control system 170 can control other properties of ion beam
192 such as the position of the ion beam on sample 180, and the
average energy of the incident ions.
[0049] In some embodiments, electronic control system 170 can be
configured to control one or more additional particle beams. For
example, in certain embodiments, one or more, types of ion beam
source and/or electron beam sources can be present. Control system
170 can control each of the particle beam sources and their
associated optical and electronic components.
[0050] Detectors 150 and 160 are depicted schematically in FIG. 1,
with detector 150 positioned to detect particles from surface 181
of sample 180 (the surface on which the ion beam impinges), and
detector 160 positioned to detect particles from surface 183 of
sample 180. In general, a wide variety of different detectors can
be employed in microscope system 200 to detect different particles,
and a microscope system 200 can typically include any desired
number of detectors. The configuration of the various detector(s)
can be selected in accordance with particles to be measured and the
measurement conditions. In some embodiments, a spectrally resolved
detector may be used. Such detectors are capable of detecting
particles of different energy and/or wavelength, and resolving the
particles based on the energy and/or wavelength of each detected
particle.
[0051] Detection systems and methods are generally disclosed, for
example, in U.S. Patent Application Publication No. US
2007/0158558, the entire contents of which are incorporated herein
by reference.
Ion Beam Measurements
[0052] In general, the accuracy of ion beam measurements depends,
in part, on the stability of the ion beam during measurement. For
example, fluctuations in the position of the ion beam on the
surface of a sample during a measurement can lead to errors in
spatially resolved measurements. If such errors are too severe, the
suitability of ion beams for certain applications can be unduly
limited. Vibrations in ion microscope systems--which can be
generated within the system (e.g., via vacuum pumps) or coupled
into the system from external sources (e.g., floor vibrations)--can
cause the tip to vibrate, producing fluctuations in the position of
the ion beam on the sample surface. Accordingly, the ion beam
systems disclosed herein include certain features that, at least in
part, help to reduce the effects of such vibrations.
[0053] FIG. 3 shows a schematic expanded view of a portion of an
ion microscope system. The system includes an outer structure 500
(e.g., a vacuum chamber) and an inner structure 510 that contacts
outer structure 500. Attached to inner structure 510 is a support
530 that supports a tip 186. During operation, as discussed above,
gas particles (e.g., helium gas particles or particles of another
noble gas) are ionized in the vicinity of tip 186, and the newly
formed ions propagate in a directly approximately parallel to a
central axis of outer structure 500. To improve the precision with
which newly formed ions are directed along the axis of outer
structure 500, extractor 550 is positioned adjacent to tip 186. As
discussed above, extractor 550 selects from among the ions produced
in the vicinity of tip 186 a certain subset of ions, which form the
microscope's ion beam. Further, the system includes radiation
shields 540 to prevent stray ions from propagating at large angular
deviations within outer structure 500.
[0054] The system also includes an intermediate structure 520 that
contacts both inner structure 510 and outer structure 500. To cool
the system (and particularly tip 186), intermediate structure 520
contacts cooler 600 (e.g., isothermically) through a thermal
contact device 560.
[0055] In general, intermediate structure 520 contacts both outer
structure 500 and inner structure 510, and is therefore capable of
cooling both structures. However, it is generally more important
that tip 186 be cooled in preference to outer structure 500,
because cooling tip 186 to very low temperature can be an important
step in operating a field ion microscope.
[0056] Tip 186 is mounted on support 530, which is typically formed
from a material such as a ceramic material. Support 530 (which can
have a thermal conductivity greater than outer structure 500) is in
thermal contact with inner structure 510, and therefore, cooler 600
can cool tip 186 by withdrawing heat through support 530, inner
structure 510, intermediate structure 520, and thermal contact
device 560.
[0057] In general, inner structure 510 and outer structure 500 are
constructed so that heat flow occurs more readily between inner
structure 510 and intermediate structure 520 (and, ultimately, to
cooler 600) than between outer structure 500 and cooler 600. In
some embodiments, for example, inner structure 510 is formed from a
material (e.g., copper, oxygen-free high conductivity copper) that
has a higher thermal conductivity than a material such as stainless
steel from which outer structure 500 is formed. The thermal
conductivity of inner structure 510 can be larger than the thermal
conductivity of outer structure 500 by a factor of 1.1 or more
(e.g., 1.3 or more, 1.5 or more, 1.7 or more, 2.0 or more, 2.5 or
more, 3.0 or more, 3.5 or more, 4.0 or more, 5.0 or more, 10.0 or
more, 100 or more, 1000 or more). The thermal conductivity of inner
structure 510 can be larger than the thermal conductivity of outer
structure 500 at room temperature, for example, and/or at
temperatures less than room temperature, including liquid nitrogen
temperature and/or liquid helium temperature.
[0058] Outer structure 500, in the embodiment shown in FIG. 3, has
a cylindrical shape with a central axis 620. Inner structure 510
has a similar cylindrical shape and shares a common central axis.
In general, the shapes of inner structure 510 and outer structure
500 can be selected as desired for particular applications and to
accommodate differently-shaped tips.
[0059] The thicknesses of each of outer structure 500 and inner
structure 510 are measured along a direction perpendicular to axis
620 in FIG. 3. In general, the thicknesses of these structures can
be selected to ensure that the thermal capacity of inner structure
510 is larger than the thermal capacity of outer structure 500.
Accordingly, in certain embodiments, the thickness of inner
structure 510 can be larger than the thickness of outer structure
500 by a factor of 1.1 or more (e.g., 1.2 or more, 1.3 or more, 1.5
or more, 2.0 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or
more, 4.5 or more, 5.0 or more, 6.0 or more, 7.0 or more, 8.0 or
more, 10.0 or more).
[0060] Typically, during operation, ions generated by tip 186 are
directed to be incident on a sample, and particles leaving the
sample in response to the incident ions are measured to determine
properties of the sample (e.g., to obtain one or more images of the
sample). During this process, vibrations introduced by cooler 600
into the system can introduce errors into the measured results. To
reduce the amplitude of vibrations introduced by cooler 600 into
the system, cooler 600 can be turned off during exposure of the
sample to the ion beam generated by tip 186. For example, in some
embodiments, cooler 600 can be operated to cool tip 186 to a
particular operating temperature, and then cooler 600 can be turned
off for a period of one minute or more (e.g., two minutes or more,
three minutes or more, five minutes or more, seven minutes or more,
nine minutes or more, 11 minutes or more, 13 minutes or more, 15
minutes or more, 20 minutes or more) while the sample is exposed to
the ion beam and particles leaving the sample are measured.
Intermediate structure 520 is typically formed from a material with
a high thermal conductivity such as copper, and forms a type of
"thermal battery" so that intermediate structure 520 acts as a
cooling reservoir when cooler 600 is turned off. In this way, the
temperature increase of tip 186 can be limited, in certain
embodiments, to a few degrees K or less when cooler 600 is turned
off.
[0061] The system includes thermal contact device 560, as shown in
FIG. 3. Thermal contact device 560 includes a first plurality of
flexible contact members 570 that are connected to intermediate
support 520 on one end, and to central member 580 on the other end.
A second plurality of flexible contact members 590 connects central
member 580 to cooler 600. One central member 580 is shown in FIG. 3
but in general, any number (e.g., two or more, three or more, four
or more, or even more) of central members 580 can be used.
[0062] Thermal contact device 560 provides a conduit for heat
transfer between cooler 600 and intermediate structure 520. Thus,
flexible contact members 570 and 590 and central member 580 are
typically formed from one or more materials with relatively high
thermal conductivity, such as copper. Other materials from which
some or all of contact members 570 and 590 and central member 580
can be formed include carbon-based materials such as carbonaceous
pitch, silver, and/or gold. In some embodiments, for example,
flexible contact members 570 and/or 590 can be formed from large
numbers of small diameter, flexible strands of one or more
thermally conductive materials such as copper, that are woven
and/or wrapped around one another to form rope-like braids
corresponding to contact members 570 and/or 590.
[0063] Thermal contact device 560 functions as a vibration damper,
reducing the amplitude of vibrations transmitted to structures 500,
510, and 520 (and also support 530 and tip 186) from cooler 600. By
forming contact members 570 and 590 from flexible materials,
vibration transfer through these materials is reduced relative to
vibration transfer through more rigid materials. Further, central
member 580 acts as a type of pendulum to counteract vibrations that
are coupled into flexible contact members 590 from pump 600.
[0064] In general, the geometric properties of flexible contact
members 570 and 590 and central member 580 are selected to
counteract the vibrational properties of cooler 600. In particular,
by selecting and/or changing the geometric properties of contact
members 570 and 590 and/or central member 580, the damping ability
of thermal contact device 560 can be specifically tuned to a
resonance frequency of cooler 600 (or higher harmonics thereof).
Typically, for example, cooler 600 has a harmonic resonance
frequency of about 46 Hz, and thermal contact device 560 can be
tuned to damp high frequency vibrations at multiple harmonics of
this resonance frequency (e.g., second harmonic and higher, third
harmonic and higher, fourth harmonic and higher, fifth harmonic and
higher, sixth harmonic and higher, eighth harmonic and higher,
tenth harmonic and higher).
[0065] The damping ability of thermal contact device 560 can be
tuned several ways. Generally, thermal contact device 560 has an
effective band of damping frequencies that includes a central
damping frequency which depends, in part, on the mass of central
member 580 and an effective harmonic spring constant of contact
members 570. In certain embodiments, to tune the central damping
frequency of thermal contact device 560, the position of central
member 580 can be selected and/or changed relative to contact
members 570 and 590 (e.g., to change the lengths of contact members
570). By changing the lengths of contact members 570, the effective
spring constant of these members can be changed, altering the
central damping frequency of device 560. In general, shortening the
length of contact members 570 makes the members stiffer, increasing
central damping frequency of device 560. Conversely, increasing the
length of contact members 570 decreases the central damping
frequency of device 560.
[0066] In some embodiments, central member 580 is implemented as a
solid cylinder, and changing the position of central member 580
relative to contact members 570 and 590 effectively corresponds to
shortening or lengthening contact members 570 during fabrication of
device 560. In certain embodiments, central member 580 is
implemented as a hollow cylinder that slides over contact members
570 and 590 (e.g., contact members 570 and 590 are continuous
members), and contact members 570 can be shortened or lengthened by
sliding member 580 along the continuous members and then securing
member 580 in position (e.g., with a fastener such as a screw).
[0067] In some embodiments, the central damping frequency of device
560 can be changed by adjusting the mass of central member 580. In
general, increasing the mass of central member 580 leads to a
decrease in the central damping frequency of device 560, while
decreasing the mass of central member 580 increases the central
damping frequency of device 560. The mass of central member 580 can
be selected during fabrication of device 560 to compensate a known
vibration frequency of cooler 600 (and/or harmonics thereof), for
example, and/or the mass of central member 580 can be adjusted
following fabrication (e.g., by adding or removing annular strips
of material that are concentric with central member 580, not shown
in FIG. 3) to tune the central frequency of device 560.
[0068] In some embodiments, either or both of contact members 570
and 590 can be shaped to reduce transmission of vibrations by these
members. For example, either or both of contact members 570 and 590
can include U-shaped bends between central member 580 and
intermediate structure 520 or cooler 600, respectively. The
U-shaped bends assist in preventing efficient vibrational amplitude
transfer along the lengths of contact members 570 and 590. Each of
members 570 and/or 590 can include multiple U-shaped bends, as
desired.
[0069] In certain embodiments, the central damping frequency of
device 560 can be changed by applying an axial rotation to members
570 and/or 590. For example, before attaching members 570 to
intermediate support 520, a torsional force can be applied to
members 570 to twist the members, so that residual torsional force
remains in members 570 after device 560 is mounted between
structure 520 and cooler 600. The residual torsional force
increases the effective spring constant of members 570, increasing
the central damping frequency of device 560.
[0070] As shown in FIG. 3, contact members 570 are attached to only
one side of intermediate structure 520. Generally, contact members
570 can be attached to structure 520 (and, in some embodiments, to
central member 580) using a deformable, thermally conductive
material such as indium foil, which fills in gaps in the mating
surfaces of contact members 570 and structure 520 and/or central
member 580, improving the thermal contact between these surfaces.
Similarly, in certain embodiments, contact members 590 can be
attached to central member 580 and/or cooler 600 via a deformable
material such as indium foil.
[0071] To achieve a relatively uniform temperature distribution
along the circumference of structure 520, structure 520 is formed
from a material that has relatively high thermal conductivity. As
shown in FIG. 3, contact members 570 are attached to only one side
of structure 520 and thus, if the thermal conductivity of structure
520 is not large enough, a temperature gradient will form along the
circumference of structure 520. In some embodiments, to reduce the
likelihood of such a gradient forming, contact members 570 can be
attached at various points along structure 520.
[0072] FIG. 4 shows an embodiment in which contact members 570 are
spaced at intervals along intermediate structure 520 (the remaining
portions of FIG. 3 are not shown, for clarity). Contact members 570
are also joined to a ring member 630, which effectively functions
in a similar manner to central member 580 in FIG. 3. Ring member
630 is connected via contact members 590 to cooler 600, for
example. By spacing contact members 570 along intermediate
structure 520, the magnitude of any thermal gradients formed in
intermediate structure 520 can be reduced.
[0073] In some embodiments, central member 580 can be attached to a
support structure. For example, central member 580 can be connected
through a support structure (e.g., wires) to outer structure 500,
or to another external structure (an external structure that is
positioned on a vibration-damping base, for example, so that it is
vibrationally decoupled from cooler 600).
[0074] When a sample is imaged by exposing the sample to the ion
beam generated by tip 186 and detecting particles that leave the
sample as a result of the incident ions, mechanical vibration of
tip 186 can lead to imaging errors. FIG. 5A shows a sample 180 that
includes a line of material 650 on the sample surface. Line 650 has
straight, parallel sides. However, if sample 180 is imaged as tip
186 vibrates (e.g., due to vibrations coupled into tip 186 from
cooler 600 and/or other sources), line 650 can appear as shown in
FIG. 5B, with wavy, irregular sides.
[0075] FIG. 6A shows the amplitude A of mechanical vibration 660 of
tip 186 as a function of time t. FIG. 6B shows an image 663 of a
sample that is exposed to the ion beam formed by tip 186. Four
image pixels 661a-d are shown in FIG. 6B. With reference to FIG.
6A, when pixel 661a is exposed to the ion beam, tip 186 is not
vibrationally displaced from its equilibrium position--the
vibrational amplitude is zero (position 662a). Accordingly,
vibration of tip 186 does not contribute any error to the position
measurement of pixel 661a. When pixel 661b is exposed to the ion
beam, tip 186 is vibrationally displaced at position 662b from its
equilibrium position. Thus, pixel 661b is measured not at its true
position, but at position 664a in the image (e.g., positively
displaced). When pixel 661c is exposed to the ion beam, tip 186 is
vibrationally displaced at position 662c from its equilibrium
position, and so pixel 661c in the image appears not at its true
position, but at position 664c (e.g., negatively displaced). When
pixel 661d is exposed to the ion beam, tip 186 is once again
positively displaced from its equilibrium position, and pixel 661d
appears in position 664d in the image. By connecting pixels 664a-d
in FIG. 6B, it is evident how the waviness and irregularity in the
sides of line 650 can be produced.
[0076] The imaging irregularities discussed above arise, in part,
from the random phase at which pixel data in the image is acquired,
relative to the vibrational motion of tip 186. To reduce these
irregularities, the pixel scanning pattern of the ion beam on the
sample can be phase-locked to the mechanical vibration of tip 186.
For example, as shown in FIG. 7, the mechanical vibration amplitude
function 660 can be phase locked to the scanning voltage 670 that
is applied to scan the ion beam across the surface of the sample.
The effect of the phase-locking is to ensure that rather than
exposing pixels 661a-d of the image at random vibrational
displacements of tip 186 from its equilibrium position, each of
pixels 661a-d is exposed with tip 186 at approximately the same
vibrational displacement from equilibrium (e.g., at points 671a-d
on amplitude function 660). As a result of the phase-locking,
dynamic imaging errors that result from phase fluctuations between
scans of certain pixels and the vibrational amplitude of tip 186
can be significantly reduced and/or eliminated.
[0077] Images can still include static errors, because different
pixels (different pixels along a common horizontal line, for
example) are sampled at different vibrational displacements of tip
186. In certain embodiments, the images can be corrected (e.g.,
following acquisition) by applying a pixel-dependent offset that is
derived from knowledge and/or estimates of the vibrational
displacement of tip 186 from its equilibrium position at each pixel
position. Due to the phase-locking between the pixel scanning
pattern and the vibrational displacement of the tip, the pixel
position measurement errors arise largely from systematic,
position-dependent errors rather than random, phase-related errors,
and are significantly easier to correct as a result.
[0078] In some embodiments, to eliminate both phase-related (e.g.,
dynamic) and static errors in images, each image pixel can be
exposed with tip 186 at a common vibrational displacement. For
example, referring to FIG. 7, each pixel in an image of a sample
can be exposed when tip 186 is at a position corresponding to
position 671a. That is, each pixel can be exposed when tip 186 is
maximally displaced in one direction from its equilibrium position.
Because the relative phase between each of the image pixels (e.g.,
not just the first pixel in each row) and the vibrational
displacement of tip 186 is the same, each image pixel corresponds
to a common vibrational displacement of tip 186 from its
equilibrium position. As a result, both dynamic and static errors
in the image due to vibration of tip 186 during imaging can be
significantly reduced.
[0079] Although simple linear raster-scanning of the ion beam on
the sample surface has been described above, in general, any
scanning pattern can be used. For example, in some embodiments,
checkerboard scanning patterns can be used, with the scanning
pattern phase-locked to vibrational displacement of tip 186 from
its equilibrium position. More sophisticated scanning patterns can
also be phase-locked to the vibrational displacement of tip 186
from its equilibrium position as discussed herein.
[0080] Another potential source of vibrational instability in the
ion microscope system is the tip manipulator, which includes a
dome-shaped surface of motion and a translator connected to tip
186, with a mating surface shaped to permit movement along the
surface of motion. The tip manipulator permits both translation of
tip 186 in the x-y plane, and tilting of tip 186 with respect to
axis 1132 of ion optics 130. FIG. 8 is a cross-sectional view of a
portion of an ion microscope system including tip 186, support
assembly 1520 and an embodiment of a tip manipulator. The tip
manipulator includes a shaft 1502, a dome 1504, a shoulder 1510 and
a translator 1514. Translator 1514 is connected to shaft 1502,
which is dimensioned to fit through an opening 1516 in shoulder
1510. Shaft 1502 is further connected to base 1508, which in turn
is connected to assembly 1520. Shoulder 1510 is in a fixed position
relative to dome 1504 by static frictional forces between surfaces
1512 and 1513, and translator 1514 is in a fixed position relative
to shoulder 1510 by static frictional forces between surfaces 1518
and 1519.
[0081] The tip manipulator provides for translation of tip 186 in
the x-y plane. To translate tip 186, a high pressure gas is
introduced into inlet 1503. The high pressure gas introduced into
inlet 1503 can be a gas such as room air, for example. Typically,
the gas can be introduced at a pressure of 50 pounds per square
inch (psi) or more (e.g., 75 psi or more, 100 psi or more, 125 psi
or more). As a result of introducing the high pressure gas, a force
is applied to translator 1514 in the -z direction, away from
shoulder 1510. The applied force lessens (but does not reduce to
zero) the frictional force between surfaces 1518 and 1519, and
permits repositioning of translator 1514 with respect to shoulder
1510 by applying a lateral force in the x-y plane. Tip 186 is
translated in the x-y plane when translator 1514 is repositioned.
When tip 186 is in its new position, the supply of high pressure
gas is turned off and strong static frictional forces between
surfaces 1518 and 1519 are re-established by evacuating the
interior of the tip manipulator using one or more vacuum pumps. Tip
186 is rigidly fixed in position as a result of the re-established
strong frictional forces.
[0082] The tip manipulator also provides for tilting of tip 186
with respect to axis 1132 of ion optics 130. To tilt tip 186, a
high pressure gas is introduced into inlet 1505. The high pressure
gas introduced into inlet 1505 can be a gas such as room air, for
example. Typically, the gas can be introduced at a pressure of 50
pounds per square inch (psi) or more (e.g., 75 psi or more, 100 psi
or more, 125 psi or more). As a result of introducing the high
pressure gas, a force is applied to shoulder 1510 in the -z
direction, away from dome 1504. The applied force lessens (but does
not reduce to zero) the frictional force between surfaces 1512 and
1513. Shoulder 1510 can then be re-positioned with respect to dome
1504 by applying a lateral force to translate shoulder 1510 in a
direction indicated by arrows 1506. Translation of shoulder 1510
corresponds to relative movement along the curved surface of dome
1504. As a result of this movement, the angle between axes 1132 and
207 (which corresponds to the tilt angle of tip 186) changes. When
adjustment of the tilt of tip 186 is complete, the supply of high
pressure gas is turned off and strong static frictional forces
between surfaces 1512 and 1513 are re-established by evacuating the
interior of the tip manipulator. Tip 186 is rigidly fixed in
position as a result of the re-established strong frictional
forces.
[0083] If the mating surfaces 1512 and 1513 are not both very
smooth, however, small protrusions on either surface can lead to
the formation of points of contact at the interface between
surfaces 1512 and 1513. In other words, as shown in FIG. 9, instead
of an entire annular contact region at the interface between
surfaces 1512 and 1513, a small number of contact points 1512a and
1512b exist between the surfaces. As a result, the frictional force
which holds tip 186 in place is greatly reduced, and external
vibrations can cause undesired motion of tip 186.
[0084] To increase the area of contact between surfaces 1512 and
1513 in the presence of surface irregularities such as small
protrusions, surface 1512 can include two or more annular
protrusions instead of a continuous mating surface, as shown in
FIG. 10. Annular protrusions 1515a and 1515b are formed in surface
1512, with a recess 1517 between the surfaces. Each of the
protrusions 1515a and 1515b has a thickness t.sub.p measured in a
direction normal to the surface of the protrusion.
[0085] Typically, the thickness t.sub.p is 1 mm or less (e.g., 800
microns or less, 600 microns or less, 500 microns or less, 400
microns or less, 300 microns or less, 200 microns or less, 100
microns or less, 50 microns or less, 25 microns or less, 10 microns
or less). Due to the relatively small thickness of protrusions
1515a and 1515b, when the interior of the tip manipulator is
evacuated, the clamping force between shoulder 1510 and dome 1504
causes each of protrusions 1515a and 1515b to deform, establishing
two regions of intimate contact with surface 1513. These regions
are annular, extending around the curved surface of dome 1504. As a
result of the annular contact regions between shoulder 1510 and
dome 1504, the frictional force that holds tip 186 in place is
greater than in the situation shown in FIG. 9, in which only
relatively small points of contact exist between surfaces 1512 and
1513. Accordingly, the stability of tip 186 is improved and the
amplitude of the vibrational motion of tip 186 can be reduced.
[0086] In the embodiment shown above, surface 1512 includes two
protrusions 1515a and 1515b, with a recess 1517 between the
protrusions. In general, surface 1512 can include any number of
protrusions (e.g., three or more, four or more, five or more, six
or more, eight or more, ten or more, or even more). Recesses can be
positioned between the protrusions to allow for deformation of the
protrusions when the interior of the tip manipulator is
evacuated.
[0087] In some embodiments, it can be desirable to improve gas
utilization (e.g., utilization of a beam-forming gas such as
helium) to increase the ion beam current, for example. Low
signal-to-noise ratio in sample measurements that are performed
with ion beams can limit the suitability of ion beams for certain
measurement applications. For example, low signal-to-noise ratios
can introduce errors in measurement precision, making such
measurements less reliable. When the ion beam is used to obtain
images of a sample, certain fine details of the sample surface can
be obscured by noise in the acquired images. One method for
improving the signal-to-noise ratio in measured images is to
increase the ion beam current.
[0088] The ion beam current can be increased by using a tip 186
with a slightly larger radius of curvature. Ionization of the gas
occurs in the vicinity of the tip apex. By using a tip with a
slightly larger radius of curvature, the region of space
surrounding tip 186 in which ionization of gas particles can occur
is larger. As a result, the ion current in the ion beam can be
increased.
[0089] Typically, to produce a tip with a larger radius of
curvature, the tip is first formed in a fabrication process
(suitable fabrication processes are discussed, for example, in U.S.
Patent. Application Publication No. US 2007/0158558). The
fabrication process can be performed in the absence of oxygen gas,
to prevent some sharpening of the tip. As a result of the
fabrication process, tip 186 typically has a full cone angle of
between 30 degrees and 45 degrees.
[0090] The radius of curvature of tip 186 is typically 100 nm or
more (e.g., 120 nm or more, 140 nm or more, 160 nm or more, 180 nm
or more, 200 nm or more). A gas (e.g., helium gas) is introduced
through a tube into cooling channels 610 in inner structure 510,
where it is pre-cooled before entering the ion microscope system
through support 530. Ionization of the gas occurs in the vicinity
of tip 186, producing an ion beam which is then directed by
extractor 550 (and, more generally, ion optics 130) to propagate
along a main direction (e.g., along axis 620 in FIG. 3) and to be
incident on a sample.
OTHER EMBODIMENTS
[0091] As an example, while embodiments have been described in
which a gas field ion source is used, other types of ion sources
may also be used. In some embodiments, a liquid metal ion source
can be used. An example of a liquid metal ion source is a Ga ion
source (e.g., a Ga focused ion beam column).
[0092] As another example, while embodiments have been described in
which an ion source is used, more generally any charged particle
source can be used. In some embodiments, an electron source, such
as an electron microscope (e.g., a scanning electron microscope)
can be used.
[0093] As a further example, while embodiments have been described
in which samples are in the form of semiconductor articles, in some
embodiments, other types of samples can be used. Examples include
biological samples (e.g., tissue, nucleic acids, proteins,
carbohydrates, lipids and cell membranes), pharmaceutical samples
(e.g., a small molecule drug), frozen water (e.g., ice), read/write
heads used in magnetic storage devices, and metal and alloy
samples. Exemplary samples are disclosed in, for example, U.S.
Patent Publication No. US 2007/0158558.
[0094] As an additional example, while embodiments have been
described in which a sample is inspected, alternatively or
additionally, the systems and methods disclosed herein can be used
to modify (e.g., repair) a sample (e.g., to repair a region of the
article at or near the portion of the article exposed by the
cross-section). Such modification can involve gas assisted
chemistry, which can be used to add material to and/or remove
material from a sample (e.g., a given layer of the sample). As an
example, gas assisted chemistry can be used for semiconductor
circuit editing in which damaged or incorrectly fabricated circuits
and/or circuit elements formed in semiconductor articles are
repaired. Typically, circuit editing involves adding material to a
circuit (e.g., to close a circuit that is open) and/or removing
material from a circuit (e.g., to open a circuit that is closed).
Gas assisted chemistry can also be used in photolithographic mask
repair. Mask defects generally include an excess of mask material
in a region of the mask where there should be no material, and/or
an absence of mask material where material should be present. Thus,
gas assisted chemistry can be used in mask repair to add and/or
remove material from a mask as desired. Typically, gas assisted
chemistry involves the use of a charged particle beam (e.g., ion
beam, electron beam, or both) that interacts with an appropriate
gas (e.g., Cl.sub.2, O.sub.2, I.sub.2, XeF.sub.2, F.sub.2,
CF.sub.4, H.sub.2O, XeF.sub.2, F.sub.2, CF.sub.4, WF.sub.6). As
another example, modification of a sample can involve sputtering.
In some instances, when fabricating articles, it can be desirable
during certain steps to remove materials (e.g., when removing
undesired material from a circuit to edit the circuit, when
repairing a mask). An ion beam can be used for this purpose where
the ion beam sputters material from the sample. In particular, an
ion beam generated via the interaction of gas atoms with a gas
field ion source as described herein can be used for sputtering a
sample. Although He gas ions may be used, it is typically
preferable to use heavier ions (e.g., Ne gas ions, Ar gas ions, Kr
gas ions, Xe gas ions) to remove material. During the removal of
material, the ion beam is focused on the region of the sample where
the material to be removed is located. Examples of such inspection
are disclosed, for example, in U.S. Patent Publication No. US
2007/0158558.
[0095] Combinations of features disclosed herein can be used in
various embodiments. Other embodiments are covered by the
claims.
* * * * *